Insulin binding and the capacity of
insulin to stimulate the conversion of
glucose to
carbon dioxide and
lipid, and to activate the
protein tyrosine kinase associated with the
insulin receptor have been investigated in adipocytes isolated from pregnant and non-pregnant women.
Insulin binding and the conversion of
glucose to
lipid were the same for both groups. However, conversion of
glucose to CO2 was higher in the non-pregnant group due to an elevated basal activity, and the increase produced by
insulin was similar in both groups. The
tyrosine kinase activity of the isolated receptor preparations was higher in the pregnant group due to an increase in the basal non-
insulin dependent activity, and the increase produced by
insulin was similar in both groups. These findings show the in vitro
insulin responsiveness of isolated adipocytes is similar for both groups, and suggests that the in vivo
insulin resistance of late pregnancy, as far as adipose tissue is concerned, is not due to any inherent defect in
insulin action at the receptor or post-receptor level. In vivo
insulin resistance may result from an increased level of circulating
insulin antagonists.